Development of the vertebrate eye requires a series of developmental events that lead to the formation of the retina and the lens, which are collectively called the eyeball. In addition to the eyeball, eye-associated structures such as the cornea, lacrimal gland, eyelid and conjunctiva are made that are required for the proper function of the eyeball. Our long-term goal is to identify developmental steps and molecular events necessary for the correct formation of each individual vertebrate eye structure. In this project, we are focusing on the development of anterior eye structures, with the primary aim to understand lens development. This proposal is a natural continuation of our previous studies investigating the role of the forkhead box-containing gene Foxe3 in lens formation, and the role of the homeobox-containing gene Rx in retinal formation. We propose the following specific aims for the next five years: Specific Aim 1 is to determine the developmental fate and gene expression of the head surface ectoderm in the absence of the retina. In wild type embryos, the lateral head surface ectoderm develops into the lens and auxiliary eye structures. In Rx-/- embryos, which have no retinal structures, the lens does not develop. The unanswered question remains whether auxiliary eye structures develop in the absence of the retina and the lens. For this reason, in the first part of specific aim 1, we will determine whether auxiliary eye structures develop in Rx-/- embryos. In the second part of this specific aim, we will characterize gene expression in lateral head surface ectoderm in the absence of the retina and compare it to gene expression in the head surface ectoderm of wild type embryos. This comparison will identify the changes in gene expression that are orchestrated by the retina, and lead to lens formation. Specific Aim 2 is to study the functional significance of the observed changes in gene expression in head surface ectoderm in the presence and absence of the retina. For this purpose, we will modify gene expression in the head surface ectoderm of Rx-/- animals and will monitor lens induction, as well as lens-specific gene expression. Formation of a lens placode will be viewed as the establishment of lens fate, and the expression of Foxe3, as the establishment of lens-specific gene expression. Specific Aim 3 is to correct the molecular and phenotypic defects in mice with mutant Foxe3 function by intrauterine gene transfer. For this purpose, we will introduce the wild type Foxe3 gene into dysgenetic lens embryos using viral vectors. These vectors will carry the Foxe3 regulatory and coding sequences of the wild type gene and will be delivered to the mutant embryos via intrauterine gene transfer. The goal of this project is to identify genes and developmental processes that are responsible for normal eye development. Identification of these genes and developmental processes will lead to the better understanding of eye diseases. As a result, new diagnostic procedures and treatments for eye diseases will be developed.